This invention relates generally to an improved process for manufacturing tongue and groove pliers. More particularly, but not by way of limitation, this invention relates to a process for forging mating surfaces on the tongue and groove pliers that interact to urge the plier members relatively together when in use.
Tongue and groove or adjustable pliers have been in use in the industry for many years. One of the disadvantages of such pliers has been the tendency to bind and damage or destroy the pivot pin or fastener connecting the plier members due to the forces generated when gripping a work piece.
This problem has been recognized, and H. H. Manning in U.S. Pat. No. 2,640,381, which issued June 2, 1953, provided for the construction pliers having mating surfaces oriented along angular planes that tend to urge the plier halves relatively together when gripping a work piece. In other words, Manning discloses the use of a "negative angle" on the mating surfaces so that the plier members are in a sense interlocking.
Manning presented a method of solving the problem of the lateral loads, that is loads that tended to break or damage the pivot pin, but his solution created a problem of to how to manufacture the pliers with such "negative angles". Generally, the pliers are forged and the forging of negative angles is an extremely difficult procedure.
The pliers, constructed in accordance with the Manning patent, has the negative angles formed by machining of the arcuate projections after forging. The machining operation is not only expensive, but it also weakens the pliers somewhat as compared to purely forged pliers.
U.S. Pat. No. 3,739,664 issued June 19, 1973 to John E. Swanstrom, Jr., describes a method of forging tongue and groove pliers with negative angles thereon. It is believed that the procedures utilized in the Swanstrom method of forming the negative angles will result in a shorter die life and thus, ultimately, increase the cost of the pliers.